67 research outputs found
Optical observations of Be/X-ray transient system KS 1947+300
ROTSE-IIId observations of the Be/X-ray transient system KS 1947+300 obtained between September 2004 and December 2005 make it possible to study the correlation between optical and X-ray activity. The optical outburst of 0.1 mag was accompanied by an increase in X-ray flux in 2004 observations. Strong correlation between the optical and X-ray light curves suggests that neutron star directly accretes from the outflowing material of Be star. The nearly zero time lag between X-ray and optical light curves suggests a heating of the disk of Be star by X-rays. No optical brightening and X-ray enhancement was seen in 2005 observations. There is no indication of the orbital modulation in the optical light curve
The Spectrum and Dips of RE 0751+14: A joint evaluation of ROSAT and ASCA Archival Data
Using archival ASCA and ROSAT observations of RE 0751+14, X-ray energy
spectra, pulse profiles and the results of pulse timing analysis are presented.
The energy spectra are well-fitted by a blackbody model at low energy and a
Raymond-Smith model at high energy, together with a partial covering absorber.
A fluorescence emission line at 6.4 keV with an equivalent width eV
was resolved for the first time.Comment: To appear on Astrophysics and Space Science, vol 259, pages 191-203,
January 199
AB Dor: A Single Star with RSCVn Like Activity in X-ray Band
Using the archival ROSAT PSPC observations, AB Dor is found to be variable in
X-rays. The periodic variations are consistent with previously reported
rotational period of 0.514 days. The average spectrum of AB Dor is best
represented with two-temperature Raymond-Smith model with kT values of
0.19+/-0.07 and 1.17+/-0.02 keV. The quiescent luminosity of the system is
found to be 4.36+/-0.6 10^30 ergs/s. A flare with a rise time of about 350
seconds is detected during which X-ray luminosity rises from 5.8+/-1.6 10^30 to
15.8+/-4.9 10^30 ergs/s. We conclude that AB Dor is very similar to the active
components of RS CVn binaries and other active classes. In view of the wide
separation from the binary companion Rst 137B, this activity must be intrinsic
to the active star.Comment: 11 pages in PostScript including figures, accepted for publication in
Astrophysics and Space Science, available at
http://astroa.physics.metu.edu.tr/preprints.htm
ROSAT Observations of the Vela Pulsar
The ROSAT HRI was used to monitor X-ray emission from the Vela Pulsar. Six
observations span 2-1/2 years and 3 glitches. The summed data yield a
determination of the pulse shape, and X-ray emission from the pulsar is found
to be 12 % pulsed with one broad and two narrow peaks. One observation occurred
15 days after a large glitch. No change in pulse structure was observed and any
change in X-ray luminosity, if present, was less than 3 %. Implications for
neutron star structure are discussed.Comment: To be publisned in the Astrophysical Journa
First hours of the GRB 030329 optical afterglow
We present the first results of the observations of the extremely bright
optical afterglow of gamma-ray burst (GRB) 030329 with the 1.5m Russian-Turkish
telescope RTT150 (TUBITAK National Observatory, Bakyrlytepe, Turkey). RTT150
was one of the first 1.5m-class telescopes pointed to the afterglow.
Observations were started approximately 6 hours after the burst. During the
first 5 hours of our observations the afterglow faded exactly as a power law
with index -1.19+-0.01 in each of the BVRI Bessel filters. After that, in all
BVRI filters simultaneously we observe a steepening of the power law light
curve. The power law decay index smoothly approaches the value ~= -1.9,
observed by other observatories later. This power law break occurs at t-t_0
=0.57 days and lasts for +-0.1 days. We observe no variability above the
gradual fading with the upper limits 10--1% on time scales 0.1--1000s. Spectral
flux distribution in four BVRI filters corresponds to the power law spectrum
with spectral index \alpha=0.66+-0.01. The change of the power law decay index
in the end of our observations can be interpreted as a signature of collimated
ultrarelativistic jet. The afterglow flux distribution in radio, optical and
x-rays is consistent with synchrotron spectrum. We continue our observations of
this unique object with RTT150.Comment: Astronomy Letters, Vol. 29, No. 9, p. 573; 6 pages, 5 figures;
pagination corrected; the original Russian version can be found at
http://hea.iki.rssi.ru/~br/030329/pfh030329.pd
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